The present invention relates to electrical rotating machines, and more particularly to the stator of an electrical machine in which the rotor is located inside the stator.
The stator has a magnetic circuit and windings of electrically conductive wires which in general are made from insulated copper wire, often round in section. The magnetic circuit, for its part, is always laminated; it is formed by a stack of magnetic metal sheets. Each metal sheet is cut to shape such that slots separated by teeth are made, the slots being the seatings for the electrically conductive wires. Each slot is delimited by two substantially radially oriented walls and a slot base, and has an opening, the opening being located on a smaller radius than the radius on which the slot base is located. This principle of arranging the stator is widely applied in synchronous or asynchronous machines.
Installing the electric windings in the slots involves inserting electrical conductors (or sections of electrical conductors) by passing them through the opening of the slot. Consider that, in the type of motor relevant here, this slot opening is oriented towards the inside and is thus hard to access. Moreover, the slot opening is in general quite narrow with respect to the width of the slot. In fact, to arrive at the optimum mechanical and magnetic construction, each tooth ends (on the side with the small radii) in a foot which partly closes the slot opening.
It is thus no simple matter to insert the electrical conductors in the slots by passing them through this rather cramped opening. This results in filling rates of the slots with the electrical conductors remaining relatively low, in particular if the electrical machine is long.
The dimensions of an electrical rotating machine depend on its rated load torque. The higher the rated load torque which a motor is able to produce, the more bulky the electrical motor, all other things being equal.
There are applications for which it is desirable to obtain both high power levels and highly compact constructions of the motor at the same time. To give just one concrete example, when the intention is to install electric traction motors in the wheels of automotive vehicles, it is desirable to be able to develop power levels of at least 10 kW per motor, and even at least 25 or 30 kW per motor for the majority of the time, for a weight as low as possible in order not to make the unsprung masses too heavy. It is also desirable for the bulk to be very small, not going beyond or going beyond by as little as possible the internal volume of the wheel so that it does not interfere with the elements of the vehicle in the event of flexing of the suspension and in the event of other types of movement of the wheel with respect to the vehicle body.
These two requirements (high power level and low weight and bulk) make it very problematic to install electric traction motors in the wheels of private vehicles without radically improving the ratio of weight to power of the electrical machines currently available on the market.